Remember all those Obama campaign emails and their, shall we say, unusual subject lines?

"Hey," wrote Barack Obama in at least five messages during the campaign.

"Hell yeah," topped one note from strategist David Axelrod.

Beyonce Knowles teased in an inbox message, "I don't usually email."

And women's rights activist Sandra Fluke provocatively reached out on "Legitimate rape."

New data released by the campaign show that these and other catchy and casual phrases were hugely successful at getting Obama supporters to open the emails and click through to donate.

Most of the $690 million "Obama for America" raised through online fundraising came from direct email appeals, according to data provided by the president's campaign exclusively to Bloomberg Businessweek and confirmed by ABC News.

The more casual and profane the tone, the campaign said, the more lucrative the blast.

Obama's "Hey" subject-lined messages were the most effective pitches of all, though the campaign did not provide a specific dollar amount.

One Obama email blast from June 26 with the subject line, "I will be outspent," raked in $2.5 million, the data provided to Bloomberg showed. Other iterations of the same message sent under different subject headings - e.g. "Thankful every day," or, "Michelle time" - were notably less successful, raking in $545,486 and $604,813 respectively.

The campaign relied on a staff of 20 full-time email writers who constantly drafted and experimented with different versions of appeals, officials said, sending them to small lists first to see what was most effective before mailing to a larger listserv of millions of names.

An October report by Return Path, an independent "email intelligence" group, found that Obama's email campaign dwarfed that of GOP rival Mitt Romney in terms of scope and effectiveness.

The study found that Obama had 13 million email subscribers - five times as many as Romney - with a 68 percent inbox placement rate (evading spam filters). Romney's placement rate was just 50 percent, according to the group, which based its findings on a random sample of 2 million inboxes between Aug. 27 and Oct. 10.

All told, by ABC News' count, President Obama sent 65 fundraising emails under his name to his campaign listserv; Michelle Obama sent 35; Obama campaign manager Jim Messina sent 34; deputy campaign manager Stephanie Cutter sent 45; national field director Jeremy Bird sent 21; and former President Bill Clinton sent 9.